This invention relates to a process for making phloroglucinal and, in particular, a process for making phloroglucinol via a novel intermediate, namely benzene-1,3,5-tris-acetoxime.
Several processes for making phloroglucinol are already known. In particular, the reduction of 1,3,5-trinitrobenzene to 1,3,5-triaminobenzene and its subsequent hydrolysis to form phloroglucinol is industrially important. According to older processes, the reduction step may be accomplished by utilizing tin in hydrochloric solution (Weidel and Pollak, Monatsh. 21, 15, (1900); Hepp, Ann. 215, 348; Organic Synthesis Coll. Vol. I, 444 (1932); U.S. Pat. No. 2,461,498), or with hydrogen and Raney nickel in an organic solvent, such as ethyl acetate (German Patent No. 813,709 ; Gill et al., J. Chem. Soc., 1753 (1949); British Patent No. 1,106,088). A reducing agent suitable for the large-scale industrial reduction of the trinitrobenzene is iron/hydrochloric acid (U.S. Pat. No. 2,614,126; Kastens, Ind. and Engin. Chem. 42, 402 (1950); British Patent No. 1,022,733). Platinum, palladium and rhodium catalysts have also been proposed for the reduction of trinitrobenzene (French Patent No. 1,289,647; Desseigne, Mem. Poudres 44, 325 (1962). In such a synthesis, instead of starting with 1,3,5 -trinitrobenzene, one can also start with 2,4,6-trinitrobenzoic acid, which on a large scale is obtainable through the oxidation of trinitrotoluene with sodium dichromate in sulfuric acid (Kastens, l.c.), since the 2,4,6-triaminobenzoic acid formed in the reduction either decarboxylates immediately to triaminobenzene, or is converted to phloroglucinol during the subsequent hydrolysis (British Patent Nos. 1,022,733; 1,106,088; 1,274,551). Furthermore, it is known to start with 5-nitro-1,3-diaminobenzene instead of trinitrobenzene (British Patent No. 1,012,782. The hydrolysis of the triamine to phloroglucinol is customarily carried out in a mineral acid solution (Flesch, Monatsh. 18, 755 (1897); German Patent No. 102,358, or, according to a more recent process, in the presence of copper and/or its salts as catalysts (German Patent No. 1,195,327).
According to a process likewise of interest from an industrial viewpoint, one may obtain phloroglucinol by oxidizing 1,3,5-triisopropyl benzene, separating the trihydroperoxide from the resulting mixture of mono-, di- and trihydroperoxides, and subjecting it subsequently to ketone splitting (British Patent No. 751,598; German Patent No. 12,239; Seidel et al., Journ. prakt. Chemie 275, 278 (1956). It is also possible to convert triisopropyl benzene directly to phloroglucinol triacetate through oxidation with oxygen in acetic anhydride, followed by hydrolysis with alcoholic sodium hydroxide to form phloroglucinol. One may also start with m-isopropyl resorcinol, which is esterified with acetic anhydride; the resulting m-isopropyl resorcinol diacetate is then oxidized to hydroperoxide and the latter is finally converted to phloroglucinol with acid (U.S. Pat. No. 3,028,410). Phloroglucinol may also be obtained, if resorcinol (Barth and Schreder, Ber. 12, 503, (1879) in 2-,4-, 5-, 3,5- or 2,4-position, resorcinol substituted by chlorine or bromine (German Patent No. 2,231,005), or 1,3,5-benzene trisulfonic acid (U.S. Pat. No. 2,773,908) are melted with excess alkali hydroxide.
In addition to the listed benzene derivatives, mention has also been made of hexahydroxybenzene, picryl chloride, tetrachloro- and tetrabromobenzene, as well as tribromobenzene, as initial materials for phloroglucinol synthesis. Hexahydroxybenzene may be hydrated with platinum oxide in an aqueous medium (Kuhn et al., Ann. 565, 1 (1949), picryl chloride may be reduced with tin and hydrochloric acid, or electrolytically, and the 1,3,5-triaminobenzene, or 2,4,6-triamino-1-chlorobenzene obtained thereby may then be hydrolyzed (Heertjes, Recueil 78, 452 (1959).
The above-mentioned tetrahalobenzenes may be subjected to ammonolysis in the presence of a copper catalyst and the intermediary triamine may be hydrolyzed in the reaction mixture without a preceding separation (U.S. Pat. No. 3,230,266). Tribromobenzene may be converted to 1,3,5-trimethoxybenzene with sodium methanolate and catalytic quantities of copper iodide in methanol/dimethyl formamide as a solvent, and also may be subsequently subjected to hydrolysis (McKillop et al., Synthetic Communications 4 (1) 43,35 (1974).
Furthermore, there is also a known phloroglucinol synthesis based on diethyl malonate. When subjected to treatment with metallic sodium, the malonic diethyl ester may condense with itself to form the trisodium salt of phloroglucinol dicarboxylic diethyl ester and this intermediate product may then be subjected to alkaline hydrolysis and decarboxylation (v. Baeyer, Ber. 18, 3454 (1885); Willstaetter, Ber. 32, 1272 (1899); Leuchs, Ber. 41, 3172 (1908); Komninos, Bull. Soc. Chem. Fr. 23, 449 (1918). Such a synthesis has been improved to the extent that the formation of the sodium malonic diethyl ester and the trisodium salt of phloroglucinol dicarboxylic diethyl ester may be performed in a single operation by means of boiling in an inert, high -boiling solvent, preferably dekalin (German Patent No. 29,998).
From the above-mentioned processes, apparently only the process based upon 2,4,6-trinitrobenzoic acid has been utilized commercially. However, such a process has several serious drawbacks. 2,4,6-trinitrobenzoic acid may be prepared by oxidizing trinitrotoluene, which is explosive, thus rendering such a process dangerous. In addition, the total yield, measured on the basis of 2,4,6-trinitrobenzene, of phloroglucinol produced via the intermediates of trinitrobenzene and triaminobenzene, is low. Such a process is also disadvantageous because the waste water formed during the oxidation and reduction is strongly acid and contains the heavy metals chromium and iron, and must therefore be treated.
A primary object of the present invention is to provide a process which is suitable for the commercial manufacture of phloroglucinol, but does not suffer from the disadvantages of the presently utilized industrial processes.